1. Field of the Invention
The field of the invention is integrated circuit-type delay lines for digital pulses, and digital frequency multipliers.
2. Description of the Related Art
Delay lines for pulse circuits can be divided into two broad categories, the first utilizing non-active devices, such as an inductor type delay line wherein an electrical pulse is inserted in one end of an inductor coil and then, after a period of time, the pulse appears at the other end. In the inductor coil-type delay, the pulse is delayed by the build up of electrical and magnetic fields surrounding the coil wherein the time delay of the pulse is an inherent electrical property of a coil. The same electrical pulse that entered the inductor coil delay line is the pulse that outputs the delay line.
The second broad category of delay lines are electronic delay lines utilizing active elements, such as transistors, in that a digital pulse is inserted at one end of the delay line and a second digital pulse, representative of the first in magnitude and duration, is outputted a specified time later. This type of time delay depends upon the inherent time delay characteristics of circuits utilizing active elements and/or electronic circuits utilizing, in addition to active elements, passive components which tend to have an effect, when properly assembled, of delaying a pulse. These passive components generally comprise resistors, capacitors, and occasionally inductors.
Now the problem with active elements utilized in digital pulse time delays is that the characteristics of the semi-conductor materials from which the active elements are fabricated change as a matter of course with rising or falling temperature, age, other environmental factors such as particle bombardment, and manufactured lot to lot variations. In addition, since most digital pulse time delay lines available today are fabricated in semi-conductor material in the form of integrated circuits of active and passive components, even the formed resistors and capacitors, and to some extent inductors, are also affected by changes in the semi-conductor material temperature, age, and other factors.
Accordingly, it is common to specify that digital pulse time delay chains are accurate at a specified temperature with their time delay varying plus or minus in accordance with the decrease or increase of their temperature.
However, while it is not always possible for a circuit designer to anticipate all the conditions under which a digital pulse time delay may operate, it is readily apparent that it would be of great value to have a delay line that an end user could rely upon to provide the time delay originally specified.
It is also readily apparent that if means were available by which a digital pulse delay line might continually calibrate itself against a standard, then an end user could be assured that the output digital pulse had been delayed the requisite time from the time of the pulse input.
Further, since the construction of the digital pulse time delay permits the precise timed output of the digital pulse, it would be useful then to devise circuitry dividing that time period into segments such a selected fraction of the original period or frequency multiplication of the input pulse signal might be obtained.
It is to these ends that the subject invention has been designed.